The preparation of various copper-containing catalysts, and the use of such catalysts in various reactions have been described previously. Such reactions include hydrogenation reactions, the synthesis of methanol and high alcohols from synthesis gas, etc. Previously known copper-containing catalysts also may contain other metal oxides including chromium oxide, zinc oxide, titanium oxide, zirconium oxide, alumina, silica, etc., and mixtures of one or more of said oxides.
The hydrogenation of carboxylic acids and carboxylic esters to alcohols is known in the art, and various methods and catalysts have been suggested for effecting the hydrogenation reaction. For example, the ester may be reduced with lithium aluminum hydride or sodium and alcohol. Another commonly practiced method involves the use of a copper-chromite-based hydrogenation catalyst. While copper chromite catalysts are commercially available and successful, the disposal of the spent copper chromite catalyst is a problem since the chromium is present in the spent catalyst. Because of stringent environmental regulations, the cost of the manufacture, use and disposal of copper chromite catalyst has increased. Thus, it is desirable to prepare copper-containing catalysts which are free of chromium.
Catalysts comprising copper, iron and a support such as alumina, and various methods of preparing such catalysts are described in a number of prior patents and publications. In one group of catalysts, iron oxide is the predominating metal oxide whereas in another group of catalysts, alumina is the predominating oxide. Catalysts wherein the copper oxide is the predominating oxide, also have been described in the prior art.
U.S. Pat. No. 4,252,689 describes a method of preparing a copper-iron-alumina catalyst by separately and simultaneously adding dropwise to a bath of water (a) an aqueous solution of cupric, ferrous and aluminum salts, and (b) an aqueous solution of an alkali metal compound effective to precipitate the copper, iron and aluminum ions, and then agitating the reaction mixture at a temperature of at least 50.degree. C. at a pH of 9.5 to 11.5 for from 10 minutes to 10 hours. The precipitate is recovered and treated to convert it to an active catalyst. The quantitative ratio of iron and aluminum atoms each to a copper atom is indicated as being preferably from 0.4 to 2.5 and 0.4 to 2.0, respectively. The patentees indicate that if the ratio deviates from the stated ranges, the catalyst obtained has small activity, and at the same time forms many by-products when used in hydrogenation. U.S. Pat. No. 4,278,567 describes a similar process for preparing a copper-ion-aluminum catalyst wherein urea is added to the aqueous solution of the cupric salt, ferrous salt and aluminum salt, and the solution is heated prior to the addition of an alkali to form a precipitate which is treated to convert it to a catalyst.
Five-component catalyst compositions are described in U.S. Pat. No. 4,551,444, and the essential components are copper, an iron group component, a component of elements 23-26, an alkali metal compound and a precious metal compound. The catalyst may be supported on alumina or silica.
U.S. Pat. No. 4,977,123 describes extruded sorbent compositions comprising mixed oxide components of copper oxide, iron oxide and alumina, and a clay binder material. The preferred combinations disclosed in Col. 6, lines 40-44 contain 1-5 copper atoms, 0-6 iron atoms and 2-6 aluminum ions. Specific examples identified are 3 CuO:Fe.sub.2 O.sub.3 Al.sub.2 O.sub.3 and CuO:Fe.sub.2 O.sub.3 :Al.sub.2 O.sub.3.
European Patent Application 320,074 published Jun. 14, 1989 describes a supported catalyst which comprises a carrier material such as alumina with copper as an active component and iron as a promoter. The proportion of iron, calculated on the amount of copper and iron jointly, on an atomic basis is no more than 25%. A process is described for preparing the supported catalyst which comprises introducing ferric ions either by injection or by electrochemical generation, optionally simultaneously with cupric ions and/or a solution of a precursor of the carrier material into a third solution or suspension wherein the pH of the solution or suspension is maintained at a value of between 4 and 7 with the proviso that if a ferric solution is injected into a suspension of a carrier already containing copper, the pH of the solution does not exceed 5.9.
Soviet Union Patent 762,964, according to an English Abstract, describes a catalyst for oxidation of carbon dioxide which can be obtained from an aluminum hydroxide gel with a pseudo-boehmite structure and a moisture content of 55-85% as the base, and treating the base with the suspension of formate, acetate or oxalate of manganese, cobalt, nickel, copper or iron or their mixtures in an amount of 0.5 to 12% by weight.
Although many copper-containing catalysts have been described in the prior art, there continues to be a need to improve the characteristics and performance of such catalysts, particularly in the hydrogenation of aldehydes, acids and esters. It is also desirable to prepare catalysts which are useful in hydrogenation reactions which can be carried out in either a fixed bed or a fluidized bed reaction.